Use of primer compositions for the cases when an adherend including a hard-to-bond material is bonded, the cases when the curing time of an adhesive is shortened, and the like, has been known since before. In general, a primer is used by applying to a subject to be adhered in advance of an adhesive, or the like, thereby a primer finally improves the adhesive strength and adhesion property of the adhesive. A catalyst and a promoter are incorporated in a primer composition as raw materials that promote the reactions of an adhesive, but since the reaction systems differ depending on respective adhesives, raw materials that are inherent to the respective adhesives are incorporated. Therefore, it is not always true that one kind of primer composition is effective for every adhesives and adherends. Furthermore, there are some cases when the compatibility between an adhesive and a primer composition should also be considered. Specific examples are the case when a primer composition and an adhesive are difficult to be brought into contact and mixed, and the like. Although the full breadth has not been clarified, there are many cases when it cannot be judged whether or not a primer composition and an adhesive can be finely used on a subject unless the primer composition and adhesive are actually used.
Patent Literature 1 describes a primer composition that is suitable for silicone rubbers. Silicone rubbers are thermosetting types since addition-reaction curable types are suitable therefor. Therefore, moisture-curable silicone rubbers which reaction systems are different are not especially described. Curable resins other than silicones are not described even they are of the same addition-reaction curable type. Therefore, it can be said that Patent Literature 1 is not substantially effective for resins other than thermosetting silicone resins. Furthermore, only the initial adhesion force was evaluated, and any reliability test was not verified.
Patent Literature 2 performs reliability tests in water vapor, oils and the like by using thermosetting silicone resins in a similar manner to that of Patent Literature 1. The contents of the reliability tests are a silicone oil immersion test (atmosphere temperature: 200° C.) and a high temperature storage test (atmosphere temperature: 230° C.), and describe that peeling off the adherend is suppressed. However, Patent Literature 2 discloses Examples, as the thermosetting silicone resins of the document, for only silicone resins using organic peroxides as a reaction initiator, and does not include any specific description relating to other adhesives. Since the thermosetting silicone resin of Patent Literature 2 is different from the thermosetting silicone resin using a platinum catalyst described in Cited Reference 1, it can be said that the primer is suitable for a thermosetting silicone resin using an organic peroxide as a reaction initiator.
Patent Literature 3 aims at increasing an adhesion effect between an adhesive and a substrate without limiting the conditions for use of a primer composition. This can be a method that decreases the effect of compatibility due to the combination of a primer composition and an adhesive as possible as mentioned above. Specifically, a primer composition is applied and then plasma is irradiated, and adhesive is finally used. However, the adhesive is a two-component silicone resin, and thus the operation is limited to an addition-reaction type using a catalyst as a reaction system. Furthermore, in the plasma irradiation, it is necessary to preset the present conditions in detail, and the number of the steps increases. Therefore, an advantage that an adhesion effect is easily obtained by use of a primer composition is lost.